Ultra-low pass filter



Feb. 17, 1959 K. w. PFLEGER ULTRA-LOW PASS FILTER 2 Sheets-Shee 1 FiledNov. 29, '1954 /oo fv ../.ow PASS OUTPUT F /LTER 1 1 4 C d 4 6.040.@ QMQNONONQO O O 0 g 000.05%0000 O 0 0 9 OOO /N VEN TOR fr. nf. PFL EGER l@324% AT TOR/VE Y Feb. 17, 1959 K. w. PFLEGER 2,874,227

v ULTRA-Low PASS FILTER Filed Nov. 29, 1954 zsheets-sneetz FIG. 3

A7' TOPNEV Application Nvember 29, 1954, serial No. '471,6859'gc'1aiins. (cl. 1t9'1o0,2)

This invention relates to ,electrical transducers of the type which Yareknown in the art as transversal filters.

The behavior of electrical networks can bespeciiied in two waysrepresenting two different physical points of view. `One is thewell-known steady-state point of view which describes the networkperformance in terms of the concepts of amplitude and phase responseVversus frequency. In fladdition to this conventionalviewpoint, there isthe time function viewpoint in which the network is described in termsof its amplitude-time response at the receiving end resulting from theapplication of an impulse of infinitesimal duration at theV sending end.Network response may thus be considered in terms of frequency or timefunctions. The bridge betweenv these two avenuesof approach is theFourier integral which may be thought of as a mathematical device forexpressing a time functio in terms of steady-state phenomena.

In general, prior art practice has been to base the `design ofcommunication networks upon the steady-state frequency amplitudecharacteristics and an elaborate theory has been developed for suchdesign procedures. The networks thus obtained contain as elements,resistances, inductances and capacitances, the frequency and/ or phaseselective effects of which are used in various combinations to securedesired responsecharacteristics.

When, however, network design is considered from the time function pointof View, that is, when time rather than frequency is taken as theindependent variable, there develops a broad group of selective circuitswhose principle of operation does not depend upon resonant combinationsof network elements.

Selective circuits embodying the time function concept have beendisclosed in Patents 2,024,900, December 17, 1935, 2,124,599, July 26,1938 and 2,128,257, August 30, 1938 to N. Wiener and Y. Lee; 2,575,393,November 20, 1951 to L. C. Peterson and R. K. Potter; 2,531,642,November 28, 1950 to VR. K. Potter, and elsewhere in the. art.

It is an object of this invention to provide certain improvements in theart of modifying given functions of time in accordance with desiredpatterns of amplitude, frequency and phase variation.

A more specific object of this invention is to utilize magneticrecording and reproducing techniques and apparatus in a novel structurefor modifying an impressed electrical input in accordance with apreselected weighting function. i

As is already known in the art, transversal filters substitute thetime-function approach for the conventional steady-state approach in thesimulation of network response, operating through a series of stepswhich include the following: Y

.(1) Recording or storing the input signal, i. e., the signal or wave tobe filtered;

(2) Delaying and weighting the stored record in accordance with apredetermined multiplying function; and

'l nited States Pater L 2,874,227 Patented Feb. 417, `1 9,59

ICC

(3) Integrating the delayed and weighted increments of the record toproduce a modified output.

Such filters utilizing a magnetic recording and reproducing system areknown in the art. The function to be filtered is recorded on a magneticcarrier or tape which is subsequently passed through a reproducing-system having a plurality of spaced pick-up points. The amount ofpick-up is varied from point to point over the pick-up interval inaccordance with a predetermined weighting function; and the weightedincrements of current from the respective points are continuously'summed to produce thedesired ltered output current., Such a filter isexemplified by lthe above-noted Patent 2,531,642 `to Potter.V

The present invention contemplates a transversal filter comprising, ingeneral, a magnetictrecording and reproducing system as in Potter, butinvolving a different structural organization of components and relyingon a part or portions of the magnetic material components to .elect thedesired weighting of stored record rather than upon transducing coils'ofparticular configurations.

In accordance with one system of the present invention, a magneticrecording ribbon, tape or wire is progressively moved past a magneticrecording device which is connected to a source of signal to befiltered. As the ribbon so moves, successive magnetic records are madetherein corresponding to the successive conditions of the signal at thetime and point of recording. The magnetic reproducing .devicev includesa core comprising a multiplicity of alternate laminations of magneticand nonmagnetic material, the core being divided into two portions orsections and including two'elongated air-gaps witha reproducing coildisposed on the core in uxlinking relationto the laminae andintermediate the elongated gaps in the core. The number of laminationsof magnetic material may be very great, that is, ofthe order of hundredsor of thousands. The recording ribbon is disposed for movement relativeto and against'the laminations lengthwise of the core and so as toprovide a magnetic path across one of such elongated gaps b'etweenopposed laminations in the core; hence, as the ribbon with its recordsof successive conditions of the signal moves over successive opposedpairs of the mag'- netic laminae, magnetic flux corresponding to themage netic condition of the record will be successively induced in thesuccessive pairs of magnetic laminae. A rotatable member, either of amagnetic material or constructed of alternate laminations of a magneticand of a nonmagnetic material, is disposed in the second of theelongated gaps in the core. If the rotatable member or rotor islaminated, the numberv and relative disposition of the laminaecorrespond to thoseV in the core. The rotor preferably includes aplurality of evenly displaced tooth or other portions extendinglengthwise of the rotor andvof the respective gap. The rotor is disposedto move .under control of the driving means provided for theiprogressivemovement of the magnetic ribbon and, in rotating relative to the laminaeforming the second gap, produces cyclical variations in the Vreluctanceof the contributions in the reproducing coil and therefore to the-output wave, that is, control of the filtering action by the system,may be provided for, in accordance with this invention, in anumber ofways. The height or the shape ofthe tooth portions of the rotor may bevaried along the length of the rotor'. Or, either or both of the airgaps, that is, the one adjacent the recording ribbon and the one inwhich the rotor is positioned, may be varied along the lengthwisedimension of the reproducing device, as, for example, by shaping orbending the magnetic laminations. Or, neither the rotor nor thelaminations need be adjusted, bent or trimmed, but a magnetic shunt beapplied to the core sections and so shaped with reference thereto as tovary the reluctance of the magnetic path ibetween individual pairs ofmagnetic laminations along the length o f the reproducing device.Control of the phases of the individual voltage contributions to theoutput wave due to the flux variations in individual magneticlaminations, may be effected by locating individual laminations of therotor, if of a toothed, laminated construction, out of phase, that is,shifted, for example, 45 degrees, with respect to other laminations ofthe rotor.

A more complete understanding of this invention will be derived from thedetailed description that follows hereinafter, taken in conjunction withthe appended drawings in which:

Fig. 1 is a side elevational view of av transversal filter of ultralow-pass type, showing also typical input and output circuit componentsthat might be associated therewith;

Fig. 2 'is a cross-sectional view of the device of Fig. l, taken alongthe line 2 2 thereof and illustrating one arrangement for obtaining thedesired weighting of stored record in accordance with this invention;

Fig. 3 is a cross-sectional view, not to scale, of a portion of anembodiment of the device of Fig. 1 taken along the line 3 3 of Fig. 2,illustrating another arrangement for effecting the desired weighting ofstored record in accordance with the invention;

Fig. 4 isan end view of a portion of a modification of the device ofFigs. 1 and 2, and Fig. 5 is an enlarged cross-sectional view takenalong the line 5 5 of Fig. 4, illustrating another structuralarrangement for effecting the desired weighting in accordance with theinvention; and

Fig. 6 is a plan view of a portion of the device of Figs. 1 and 2, takenalong the line 6 6 of Fig. 2, illustrating still another arrangement bywhich the desired weighting in accordance with the invention may beobtained.

The transversal filter of the drawings comprises an endless magneticrecord carrier, tape, ribbon or wire 10 driven by any suitable drivingmeans, for example, the motor 12, through suitable gearing and shafting14, 16, 18, 20, the record tape passing over the driving pulley 22 andidler pulley 24 at constant velocity. To simplify the disclosure, allshaft `bearings have been omitted. The record carrier may be of anysuitable material, preferably one adapted to be uniformly coated orimpregnated with magnetic material. An electromagnetic recorder orrecording device 26 is disposed in transducing relation adjacent theupper outer surface of the magnetic carrier in the region in which thecarrier approaches the idler pulley. The recording device is connectedto a source 28 of electrical signal. This electrical signal is to befiltered in its transmission through the transversal lter of theinvention, and, for purposes of illustration, may consist of a very lowfrequency signal wave including undesirable signal content, for example,noise, of frequency or frequencies close to that of the signal wave andof such low order as not to permit the use of any simple electrical lterto separate such undesirable signal content from the signal wave. Forexample, in a particular envelope delay measuring and recording set inwhich the delay indicating current is a slowly varying direct currentfed to the indicating meter or recording device of the set, theinterposition of a filter just ahead ofv such indicating meter orrecording device and havinga cut-off at somewhere between .003 and .0155cycle per second in order to reduce random noise reaching the indicatingmeter or recording device, has been considered desirable. As themagnetic carrier moves progressively under control of the driving meansin transducing relation to the recording device, the magnetic materialin such carrieris magnetized along 4 its surface transversely to thedirection of motion of the carrier, the successive magnetic records inthe carrier corresponding to the successive conditions of the signalinput from the electrical source at the time and point of recording.

The transversal filter also comprises an electromagnetic reproducer orreproducing device 30. This device includes a core of a large number ofthin alternately assembled laminations 32, 34 of magnetic andnon-magnetic material, respectively, the core being divided into twosubstantially L-shaped sections or portions 33, 35 so as to provide ordefine two elongated air gaps 36, 38 extending lengthwise of the core,that is, in the direction of motion of the magnetic carrier. The gap 36is formed by the opposed extending portions 40 of oppositely disposedlaminations in the core sections, and a 'magnetic flux path between eachopposed pair of the laminations of magnetic material is completedthrough the magnetic carrier which preferably is so disposed as to beprogressively moved over the upper edges or surfaces 42 of thelaminations in sliding or frictional contact therewith, as indicatedmore clearly in the cross-sectional view of Fig. 2. Hence, as themagnetic carrier with its records of successive conditions of theelectrical signal input moves over successive opposed pairs of themagnetic laminae, magnetic flux corresponding to the magnetic conditionof the carrier will be successively induced in the successive pairs ofmagnetic laminae.

Each lamination of magnetic material is thin and, although not shown inproportion in the drawings, may be of the order of .001 inch inthickness, with the interposed spacers or laminations of non-magneticmaterial of the same order of thickness. Each core portion may compriseshundreds or even thousands of these laminations suitably fastenedtogether, for example, by bolts 44 of non-magnetic material, into asingle solid member. Each core section 33, 35 is surrounded by a winding37 located intermediate the gaps 36, 38 and the windings are connectedin series aiding to the input of an electrical wave amplifier 39. In thecross-sectional View of Fig. 2, when the magnetic flux has the directionshown by the arrows, the wires having current leaving the plane of thepaper are indicated as dots and those having cur rent entering the planeof the paper are indicated as crosses. The output of the amplifier isshown connected through a rectifier 41 and a conventional low-pass lter43 of simple electrical type to a utilization circuit or device 45. Fora purpose to be explained at a later point in this description, themagnetic laminations may be provided with a portion of reduced section,for example at 46, and a suitably elongated slot or hole 48 for thelower of the fastening devices 44, so that the lower end portions of oneor more of such laminations may be adjusted or bent in position, asindicated by the dotted line, so as to change, lamination by laminationif desired, the cross-dimension of the gap 38.

The gap 38 contains a rotatable member or rotor 50 extending lengthwiseof the gap, and including a plurality of evenly displaced projecting,ridge or tooth portions 52 extending lengthwise of the rotor and of thegap. The rotor is adapted to be rotated, as indicated, under control ofthe driving means 12, and, in rotating relative to the laminae formingthe gap 38, to produce cyclical variations in the reluctance of themagnetic flux paths through such laminae and the rotor, therebyperiodically increasing and decreasing the effect of the gen- 'erallylimited or small amount of the flux induced in the minute', if, forexample, this should be selected asrof .'ing coil .for each suchupairofv laminations.

rtlzleorder of 1800 revolutions .per minute, .andthe lrotor .'has `fourlongitudinally. extendingridgesor teeth as shown, Ithe cyclicalivariations in .flux vintroduced vthereby would .use of a greatervarietyof.liltercharacteristics as will -,age canA be inducedin thewindings 37. -T he total voltage impressed 4on the ampliiier 39-s theresultant of the etects due to each pairofmagnetic laminations. Thelarger .the number ofsuch voltage `contributions closely spaced, thecloser is the effect obtained of a substantially continuous pick-up ofthe stored signal on the carrier and the farther apart-in 'frequency arethe spurious passbands which occur. due to use of a finite number ofpickups. For example, it is estimated, based on experiment, that if `atransversal filter has a useful-pass-bandof .03 cycle per second andif-as `many as 7100 laminations of -magnetic-material are assembled in`each core section,

the spacing between suprious pass-bands would be of the order of about130 cycles per secondgvhence the low-pass -lter -43 need have aout-offvonly of about -100 cycles per second, which would also eliminatepulsations due to the rotor.

The suitable weighting in the-reproducing vdevice in accordance withtransversal filter theory -may be accomplished for each separate pair ofopposed magnetic laminations by adjustment of its magnetic pathreluctance.

One method-'is to adjust air gaps between the teeth or ridges of therotor andthe laminations 32. Oneway inwhich this may bedone-is asfollows: A-rotor initially :shaving uniform .toothtorridge heightthroughout its length is mountedasshown Vin the drawings. The carrier.or tape is removed-and a thin, needle-like permanent magnet .is placed.on the pick-up surfaces 42 of a particular pair -of lmagneticlaminations. Then using a cutting tool, as the rotor is caused torotate, the height of each tooth or ridge is reduced in the regionthereof opposite the particular pair of laminations until the output ofthe reproducing device is downthe .desired number of decibels with.respect toa maximum value prior to the cutting or trimming operation.in this manner, the rotor is shaped `at each point along its lengthcorresponding toa pair .of magnetic laminations so as to give thedesired amplitude contribution in the reproduc- If at any point, thevrotor ridge is cut away completely, .there .would be substantiallyZeroV pick-up in the coil -due to v:the laminations corresponding tothat point.

tion in spacing between correspondingly located lamina- .tions 32, .32.and v314,34 in the core sections and in `the rotor.

rWhen the rotor is rassem'bledlof; alternate laminations vof magneticandnon-magnetic material and theiridges or .teeth are sinusoidal,instead` of substantiallyrectanglilar as shown in the drawings, certainof the laminations may .be displaced fby mounting them 45 degrees withrespect to the others. Then tooth portions occur where spaces had beenand `vice versa. The voltages .generated in .there-- producing coil bythe displaced laminations will be degrees out yof vphase with respect tolthose generatedby the other laminations and will add in phase.oppositionin the coil windings. This sort of phase shift gives theefectnecessary Ito simulate a ,lter vwhose response .due to animpulsehas oscillations with signreversals. In the case of suchsinusoidal configuration .for the teeth .or ridges, their etfects wouldbe interfered withif they .were cut or trimmed for weighting purposes,`and the adjust .ment in the air gap wouldbe accomplished vbymeansdescribed hereinafter.

When-the `input .electrical signal (i. e., desired signal wave plusrandom noise) Vis predominantly unidirectional so that the desiredoutput wave .when .ltered never changes sign, the amplifier 39 may bearranged to feed its output into a linear rectifier 41. 1f, however, the.desired output wave issupposed .to change sign ever, the linearrectiercould be replaced by a:homodyne detector. -The local carrier for thisdetector would be .120 cycles per second from a generator (not shown).that could be connected .to the shaft 54, in phase with the.l20 cyclesper ,second pulsations in theampliier during positive outputs therefrom.

It is desirable thatthe magnetic carrier or .tapeshall pass over thepolefaces 42 of each lamination without appreciable wear while at `thesame .time wiping them closely. Therefore, the surfaces of thesepolefaces, the non-magneticlaminations or spacers .andthe solidnonmagneticspacer member occupying the gap 36, on which the tape wipes, 'should behighly polished. Tohold the tape .flat against the pole-pieces, a longilat polished -horizontalshoa not shown, could be provided within thespace between the pulleys 22, 24 so as to bearagainst the inner sideofthe tape as the latter moves through the reproducing device.

In most laminated magnetic core structures, the separation between thelamination-s of magnetic material is merely for the purpose of reducingeddy currents, and might be provided by.a verythin coating of a cement.In the system herein disclosed, it is also desired to .secure a certainamount of magnetic separation between laminations. In .an ideal casethere would be no flux leakage from one pair of laminations to another.In actual practice, however, this ideal will not be attained althoughdeparture from it could beminimized 4by increasing the thickness of thespacers or alternate laminations of non-magnetic material. Since thenature of the recorded electrical signal input will lbe such as usuallyto produce a slowly varying magnetomotive force along the tape, the willbe little diiference between the ilux in adjacent magnetic laminationsand little tendency for flux leakage. The error, if any, introduced bysuch leakage-should be of negligible order when the alternate magneticand non-magnetic laminations are of about equal thicknesses.

In accordance with conventional magnetic recording technique, thetransversal'lter system described may include an erasing device forrestoring themagnetic carrier to a non-magnetized condition after theportion on which signal input has been stored by therecording device hastraversed the reproducing device and, having passed over the pulley 22,approaches the recording device, whereby va .tape of moderateproportions may be utilized for an extended ltering operation. Likewise,in accordance with conventional magnetic recording technique, a highfrequency biasing current may be impressed on the recording device'simultaneously with the electrical signal input. Another method ofvarying the spacing between the rotor teeth and the laminations of thecore sections to accomplish the desired weighting of the contributionsof the individual magnetic lamination pairs to the induced voltage inthe reproducing coil, in which cutting or trimming of the rotor isunnecessary, will now be described with reference to the reduced-sectionportions 46, Fig. 2, of the laminated core sections. The portions 46 ofreduced section and the 'slots 48 permit the individual laminations tobe adjusted or bent toward or away from the rotor. If the adjustment ofthe laminations requires a displacement greater than reasonably sized`slots would allow, the lower fastening devices 44 could be removed andanking plates (not shown) at the ends of the core sections could be'secured together using bolts extending below the lower ends of thelaminations, thus holding the adjustment xed. Of course, the laminationscould be made longer Vthan shown, that is, below the portions of reducedsection, with the rotor located farther below the reproducing coil thanshown. In such event, a very small bend or adjustment at the portions 46would result in a large displacement at the ends opposite the rotorteeth.

Another arrangement to control the amount of pickup along the lengthwisedimension of the reproducing device, if it is desired to leave the rotorand the laminations adjacent thereto unaffected, is to vary thereluctance across the gap 36 by cutting or 'trimming opposed pairs oflaminations. This practice is illustrated in Fig. 6.

An alternative to cutting or trimming the rotor, or the opposed pairs oflaminations of the gap 36, or to bending or adjusting the laminationswhere adjacent the rotor, is to add a magnetic yoke to the structure,which yoke would function to shunt the magnetic path between |opposedpairs of laminations in the core sections and whose shunting effectwould be adjustable over the lengthwise dimension of the reproducingdevice.

Such a magnetic shunt could be readily applied when the core sectionsare constructed so that the lower ends thereof extend below the rotor,as illustrated in Figs. 4 and 5. The magnetic shunt comprises a thinplate member 60 of magnetic material having angle portions 62 adapted toengage the ends of the core sections 33, 35, a fragment of only one ofwhich is shown in Fig. 5. The plate is bent or otherwise shaped orrippled to provide the desired varying distances lengthwise of the plateand the laminations of the core sections so as to elfect the desiredweighting of the contributions of the individual pairs of laminations tothe voltage induced in the reproducing coil. The pairs of laminationswith which the plate makes contact are short-circuited magnetically,lwhile those from which the plate is spaced are short-circuitedmagnetically to a degree dependent on the spacing, the greater theseparation, of course, the less the short-circuiting effect of theplate. It will be evident that this expedient also offers a means forreadily obtaining a variety of filter characteristics inasmuch asshunting plates of differing contours along the lengthwise dimension ofthe core sections may be made available for substitution for oneanother. ing some complication in structure, it would be possible toform a exible magnetic shunting plate the irregularities in which forshunting purposes are controlled by micrometer screw adjustments heldrmly in place by lock nuts (not shown).

The axial or lengthwise play of the rotor should be negligible in thecase of ridges or teeth having adjusted heights. When, however, theweighting is accomplished by adjusting the reluctance at the gap 38 'bybending the laminations with respect to the rotor or by utilizing themagnetic shunting plate, axial play of the rotor is not significantexcept where one or more parts-of the rotor have teeth shifted 45degrees as noted hereinabove. In the latter situation, axial play shouldbe severely limited. The use of a worm gear, as shown, near the motor12, tends to reduce any such axial play.

Although this invention has been disclosed with reference to a speciiicstructural embodiment and certain Although involvvariations therein, itwill be evident to the skilled in the art that the invention is notrestricted in scope thereto but is capable of other embodiments withoutdeparting from the spirit of the invention.

What is claimed is:

l. In a magnetic recording-reproducing system, in combination, amagnetic recording tape, an electromagnetic recording device, drivingmeans to progressively move said magnetic recording tape in transducingrelation to said recording device, an electrical signal source, saidrecording device being coupled to said signal' source whereby magneticrecords of said signal corresponding to successive conditions of saidsignal are impressed on said recording tape by said recording devicesuccessively in adjacent regions along the tape in its direction ofmotion, but with lines of force running transversely to the direction ofmotion, an electromagnetic reproducing device disposed to respond to themagnetic records of said tape, said reproducing device including a corecomprising a large number of thin laminations of alternately magneticand non-magnetic material, said laminations being perpendicular to thedirection of motion of the tape, said core including a pair of elongatedgaps which cut a plurality of said laminations transversely, saidreproducing device constituting a multiplicity of reproducer unitslocated in adjacent succession in the direction of motion of the tapewhereby each transversely magnetzed region of the tape passes over eachof said reproducer units to produce signals from the tape simultaneouslyat its various successive transversely magnetized regions distributedalong the length of the tape in the direction of its motion, some atleast of said reproducer units having different magnetic reluctancesvarying along the length of said reproducing device in accordance with apredetermined weighting function, said driving means being disposed tomove said recording tape progressively in transducing relation to therst one of said gaps in said reproducing device and in a directionparallel to the long dimension of said one gap, a reproducing coil forsaid multiplicity of reproducer units disposed in ux-linking relation tothe magnetic laminations of said core and surrounding said coreintermediate said elongated gaps, and an output circuit in energytransfer relation with said reproducing coil.

2. A system in accordance with claim 1 in which a rotor member isdisposed within the second of said elongated gaps of said core anddriven by said driving means to cyclically vary the reluctance of thepath through individual pairs of the magnetic laminations of said core,and in which some at least of such magnetic laminations are adjustablein position where adjacent to such rotor member to provide saiddifferent reluctances.

3. A system in accordance with claim l in which a rotor membercomprising alternate laminations of a magnetic material and anon-magnetic material is disposed within the second of said elongatedgaps in said core and driven by said driving means relative to thelaminations forming said second gap to cyclically vary the reluctance ofthe path through individual pairs of the magnetic laminations of saidcore and in which two or more of the laminations of said rotor are inrespectively different relative spacing from magnetic laminations ofsaid core correspondingly located lengthwise of said second gap.

4. A magnetic transducer comprising in combination a hollow corecomprising a stack of alternately magnetic and non-magnetic laminaehaving two gaps therein extending through said laminae lengthwise ofsaid stack and dividing the core into two portions, said stack oflaminae constituting a multiplicity of magnetic reproducer units locatedin adjacent succession, a magnetic recording tape bearing a signalrecord in the form of adjacent regions along the tape in its directionof motion which are magnetized transversely to said direction, saidlaminae being perpendicular to said direction, said core being disposedwith the laminae forming one of said gaps in transducing relation withsaid magnetic tape and extending in said direction, driving meansdisposed for progressively moving said tape in transducing relation withthe laminae of said one gap so that each transversely magnetized regionof the tape passes over each of said reproducer units to produce signalsfrom said tape simultaneously at its various successive transverselymagnetized regions distributed along the length of said tape, arotatable magnetic member disposed in the sec ond of said gaps in spacedrelation to the laminae forming said second gap, the spacing of saidrotatable member and said laminae varying along the length of said core,and a reproducing coil disposed on said core in ilux-linking relation tosaid laminae and intermediate the elongated gaps in said core.

5. A magnetic transducer as claimed in claim 4 in which the variablespacing between said rotatable member and the laminae of the respectivegap is determined by variation in contour of said member lengthwisethereof.

6. A magnetic transducer as Iclaimed in claim 4 in which the variablespacing between said rotatable member and the laminae of the respectivegap is determined by the positions of adjustable portions adjacent saidrotatable member of some of said laminae.

7. A filter system comprising an input circuit, an output circuit, amagnetic recorder and a magnetic reproducer disposed at spaced pointsalong a movable magnetic record carrier in wave transducing relationtherewith, said recorder being adapted to record at respectivelysuccessive points along the length of said magnetic record carrierwhereby an electrical signal appearing in said input circuit is recordedin its successive conditions on successive adjacent portions along saidmagnetic record carrier in its direction of motion but 1() with lines offorce running transversely to said direction, said magnetic reproducercomprises a unitary structure having a multiplicity ef distinct spacedmagnetic transducing portions arranged in adjacent succession in thedirection that the record carrier moves, all coupled to said outputcircuit through a reproducing coil common to said multiplicity ofportions so that the successive adjacent transversely magnetizedportions of said record carrier pass over each of said transducingportions in succession for simultaneous production of signals in saidtransducing portions at points distributed along the length of therecord carrier in the direction of its motion whereby the signalreproduced by each transducing portion is in time-displaced relationwith the signal reproduced by each of the other transducing portions andis integrated in said common reproducing coil, said transducing portionshaving different magnetic reluctances varying along the length of saidunitary structure in accordance with a predetermined weighting function.

8. A system in accordance with claim l which includes a yoke of magneticmaterial between the ends of the laminations forming the second one ofsaid gaps, said yoke being spaced from the ends of certain of thelaminations by different distances to provide the different reluctancesin accordance with the weighting function.

9. A system in accordance with claim 1 in which the ends of the opposedpairs of laminations have different spacings across said irst gap toprovide the different reluctances in accordance with the weightingfunction.

References Cited in the le of this patent UNITED STATES PATENTS2,423,339 Newman July l, 1947 2,517,808 Sziklai Aug. 8, 1950 2,531,642Potter Nov. 28, 1950 2,641,656 Dicke June 9, 1953

